Tilting progressives

[drk]

I think it's generally rough to wrap progressives, as it narrows the corridor down near nothing and narrows the near zone (pretty narrow on higher adds, who really like progressive sunwear).

Additionally, wrap compensation can't be done to the entire lens, just one zone (logically the distance zone).

Solutions are traditional faceform, only, for serious progressives, FT segments, instead, even individualized progressives to maximize zone width that you are about to minimize by wrapping.

What I think I believe is this:
If the corridor is going to effectively disappear, you'd better get into the near zone quickly. That means short corridor design.

Having said that, shorter corridor designs tend to have unwanted astigmatism in the distance zone, which when wrapped will really screw with the distance vision.

The ideal design to wrap would have a clear distance zone and a high/wide near zone with a short corridor. I suppose that would necessitate a higher amount of unwanted astigmatism in the lower portion of the lens. That sounds like a hard/short corridor.

And we'd like polycarb, huge blanks, and polarization to boot.

Can anyone think of what fits the bill?

[Uilleann]

How wrapped and how large a lens are you talking? We've had plenty of success with Maui in the progressive dept., Mind you, there are logical limits even then concerning power, wrap and decentration. But a little fore-planning, and setting up very realistic expectations with your patient will help immensely in my own experience.

[braheem24]

While 18mm is not a short, Image has very little if any noticeable astigmatism above the 180 and available in pretty much everything.

Augen several short pals in trivex including an 8mm shorty.

[blinkvelo]

Move in to a Wrap designed lens to start with. Shamir autograph Attitude has the design and choices for you. Use the Trivex or 160 for a much nicer lens material than crappy poly. The same design is used in NXT tinted trivex and Kaenon Polarized. An that is the design Maui uses in there best lens.

[Darryl Meister]

If you use a free-form progressive lens that has been truly optically optimized for the position of wear, including thw wrap angle, and not just a lens (free-form or semi-finished) that has had only basic prescription compensation applied, you can maintain the intended width of the intermediate zone. This is the best solution for wearers in wrap frames.

Best regards,
Darryl

[drk]

Thank you all for responding.

Darryl, without being too proprietary, here, I'm going to ask you to help me understand.

When designing a program that compensates progressives for lens tilt, can you compensate point-by-point from the distance zone through the corridor into the near zone? I'm guessing "yes". Clearly we can't do that with a home-made lens-tilt formula Rx compensation, as you say.

When designing a program that compensates progressives for lens tilt, can you pretty closely replicate the lens performance of a 8-degree wrap POW when faced with a 20-degree wrap POW, or is it going to be intrinsically inferior? I'm guessing inferior, and that a program may indeed widen the corridor and near zone, but not without other sacrifice.

[Darryl Meister]

When designing a program that compensates progressives for lens tilt, can you compensate point-by-point from the distance zone through the corridor into the near zone? I'm guessing "yes". Clearly we can't do that with a home-made lens-tilt formula Rx compensation, as you say

You can write a program that optically optimizes the lens design on a point-by-point basis. This is an extremely complex process that often requires finite element method combined with bivariate splines, or mathematical fitting functions.

Essentially, the prescription errors caused by the optics of the lens and the position of wear at each specified point are calculated and then compared to the target or ideal lens design. Next, the surface curvatures are locally fine-tuned at each point in order to correct or at least minimize these prescription errors by manipulating the surface curves mathematically. Since a "real" surface can generally not achieve the desired correction at every point, this process is repeated until the new surface curvatures result in a real, continuously smooth surface that comes as close as possible to achieving the desired optical performance of the target lens design.

The final result of this optimization routine is a lens that delivers the intended performance of the progressive lens design, regardless of the prescription or position of wear. Although high prescription powers and extreme positions of wear may necessitate slightly higher levels of peripheral astigmatism than lower powers or more conservative fitting geometries, a well conceived optimization process will come extremely close to delivering the intended optical performance of the target design.

Unlike optical optimization, basic prescription compensation simply corrects the prescription errors at only one point, typically corresponding to the center of the distance zone, often using relatively simple mathematics. This leaves residual optical errors in the lens periphery and, in the case of progressive lenses, the corridor and near zone. The comparison below depicts the performance of -3.00 D progressive lenses in a "wrap" frame using a standard semi-finished 8 Base, a standard semi-finished 8 Base with basic prescription compensation, and a fully customized free-form 8 Base.

Best regards,
Darryl

[drk]

The final result of this optimization routine is a lens that delivers the intended performance of the progressive lens design, regardless of the prescription or position of wear... a well conceived optimization process will come extremely close to delivering the intended optical performance of the target design.

You know, that's a pretty cool achievement; one that's not intuitively possible, to me.

I appreciate the in-depth response.

I'm thinking, as a general rule, then, that all weird progressive things will go individualized.

[xiaowei]

(Attached thumnails of tilt-compensated nand uncompensated PAL surface astigmatism)

Hi, very interesting info. I was wondering, BTW, what is the reason for the "fine structure" of the results, i.e. the multiple "islands" and "bays" in the astigmatism surface? As I assume this is based on ideal design data, it cannot directly be manufacturing error. However, it is probably manufacturing related, are these "bumps" caused by the final representation of the surface by a system of functions with a limited number of coefficients (some kind of polynomials, but liekly no Zernikes), i.e. is it some remaining "ringing" whentrying to find the coeffs that best fit the "perfect" surface.

Sincerely

[Barry Santini]

With regard to wrap progressives and intermediate utility, and beyond the finite lens design and optimization analysis, another significant factor is setting the corridors properly within the frame. Here, the following comes also into play:

1. Errors resulting from inaccurate/imprecise PDs; i.e., miscalibrated or misused pupilometers
2. Disparities resulting from mismatch between pupilometer "resting"/reference points and the acutal frame fit
3. Disparities resulting from differences in pupilometer vs. frame fitted vertex distances
4. Errors resulting from lack of PD compensation when using traditional blockers during conventional edging
5. And don't forget the newbie on the block. adherence to Gerstman calculations for compensating DV Rx and prismatic influences on corridor placement.

If your wrap progressives are working out (?!), and you have not vetted any of the above, it just goes to show you that pigs can fly!

B